The present invention relates to a control circuit for driving a capacitive display unit such as an EL display panel.
Recently, a new fact has been discovered that a certain type of the light-emitting elements such as ZnS thin-film light-emitting elements exhibits hysteresis behavior in its light emitting mechanism. Thus, utilization of such hysteresis behavior makes it possible to provide the light-emitting elements with memory capacity so that a matrix of such light-emitting body may provide character display functions in a two-dimensional manner.
A typical drive system for the above-mentioned matrix panel is disclosed in, for example, U.S. Pat. No. 3,946,371 to Kenzoo Inazaki, Yoshiharu Kanatani, Masahiro Ise, Etsuo Mizukami and Chuji Suzuki, entitled "DRIVE SYSTEM FOR MEMORY MATRIX PANEL", issued on Mar. 23, 1976.
In such a drive system, an alternating sustaining pulse is required to be applied to the whole area of the display panel in order to maintain the light-emitting condition of the written position or the erased position. As is well known, the thin-film EL element is a capacitive display element, and the total capacitance of the display panel is considerably high when a large display panel is fabricated. When such a large display panel is driven through the use of conventional CR charging and discharging switching technique, a large transient current flows through the display element. This will damage the switching elements and electrodes formed on the thin-film EL display panel. It is required to limit the transient current without increasing the power dissipation. Such problems occur not only in the EL display panel but also in usual capacitive display units, such as a plasma display unit and a liquid crystal display unit, which have an insulating display layer sandwiched between a pair of electrodes.